The network data management protocol (NDMP) specifies a common architecture for the backup of network file servers and enables the creation of a common agent that a centralized program can use to back up data on file servers running on different platforms. By separating the data path from the control path, NDMP minimizes demands on network resources and enables localized backups and disaster recovery. With NDMP, heterogeneous network file servers can communicate directly to a network-attached tape device for backup or recovery operations. Without NDMP, administrators must remotely mount the network-attached storage (NAS) volumes on their server and back up or restore the files to directly attached tape backup and tape library devices.
Tape devices are one conventional approach for enabling recording of block-based backup data. A tape device provides sequential access storage, unlike a disk drive, which provides random access storage. A disk drive can move to any position on the disk in a few milliseconds, but a tape device must physically wind tape between reels to read any one particular piece of data. In tape devices, a disadvantageous effect termed “shoe-shining” occurs during read/write if the data transfer stops or its rate falls below the minimum threshold at which the tape drive heads were designed to transfer data to or from a continuously running tape. In this situation, the modern fast-running tape drive is unable to stop the tape instantly. Instead, the drive must decelerate and stop the tape, rewind it a short distance, restart it, position back to the point at which streaming stopped and then resume the operation. If the condition repeats, the resulting back-and-forth tape motion resembles that of shining shoes with a cloth. Shoe-shining decreases the attainable data transfer rate, drive and tape life, and tape capacity.